I read Event Details, And I deside join the jam–72 hour deadline, But my English is not good, and the description mentions :opting out of the Graphics or Audio categories if yours isn’t original.

What does this mean? Can I use assets under the CC0 license?

If I use assets under the CC0 license, do I need to indicate which assets are not my original work?

I don’t quite understand what opting out means.